1. Field of the Invention
This invention relates to solid electrolytic capacitors having a resin outer package.
2. Description of Related Art
FIG. 17 shows in cross section the structure of a conventional solid electrolytic capacitor.
As shown in the figure, a conventional solid electrolytic capacitor 120 has a capacitor element 106 that includes: an anode 101 made of a valve metal; an anode lead 102 provided in the anode 101 and having one end 102a embedded in the anode 101 and the other end 102b extending from the anode 101; a dielectric layer 103 formed by anodizing the anode 101; an electrolyte layer 104 formed on the dielectric layer 103; and a cathode layer 105 formed on the electrolyte layer 104. The anode 101 and the anode lead 102 are joined and integrated together by embedding the anode lead 102 into a powdered mass of a valve metal to extend the other end 102b of the anode lead from the powdered mass, pressing the powdered mass into the shape of an anode 101 and sintering it.
Furthermore, an anode terminal 107 is attached to the other end 102b of the anode lead 102, and a cathode terminal 109 is attached to a surface of the cathode layer 105 with a conductive adhesive 108. The solid electrolytic capacitor 120 is formed through a molding process including: setting of the capacitor element 106 in a mold for resin molding with the anode terminal 107 and cathode terminal 109 fixed; and encapsulation with a resin outer package 111. In this molding process, a resin for forming the resin outer package 111 is poured into the mold for resin molding.
In such a solid electrolytic capacitor 120, the anode 101 and the anode lead 102 are joined and integrated together. In joining the anode 101 and the anode lead 102, defects and strains are likely to be produced particularly in the anode 101. The dielectric layer 103 is a self-oxidation film formed by anodizing the anode 101. Therefore, if anodization is done with defects or strains produced in the anode 101 as above, defects or strains are also likely to be produced in a part of the dielectric layer 103 located in the vicinity of the region in which the anode 101 and the anode lead 102 are joined together. In addition, the part of the dielectric layer 103 in the vicinity of to the region in which the anode 101 and the anode lead 102 are joined together is susceptible to stress transmitted from the anode lead 102 in the molding process, whereby the dielectric layer 103 is likely to produce defects, such as cracks.
A technique for coping with the above problem is disclosed in Published Japanese Patent Application No. 2001-203128, in which a root 102c of the anode lead 102, which is a part at which the other end 102b of the anode lead extends from the anode, is covered with a thermosetting resin to hold the anode lead rigidly. According to this technique, stress applied from the anode lead to the dielectric layer in the molding process can be reduced. Therefore, in the solid electrolytic capacitor disclosed in the above document, the occurrence of cracks in the dielectric layer can be reduced and the leakage current can thereby be reduced.